Myotonic dystrophy (hereinafter sometimes referred to as “MyD”) is the most common myopathy in adults. MyD is an autosomal dominant multi-organ disorder which affects skeletal and smooth muscles as well as eyeballs, heart, endocrine system and central nervous system, and its symptoms are diverse, including muscular atrophy, muscle weakness, muscle contraction (myotonia), cataract, insulin resistance, hypogonadism, cardiac conduction defect, frontal baldness, intellectual disability, etc. (Non Patent Literature 1). MyD has two types: type I (MyD1) resulting from abnormal expansion of a CTG repeat in the 3′-UTR (3′-untranslated region) of the dystrophia myotonica protein kinase (DMPK) gene (Non Patent Literature 2 to 4); and type II (MyD2) resulting from abnormal expansion of a CCTG repeat in intron 1 of the Zn finger protein 9 (ZNF9) gene (Non Patent Literature 5). In each type, a particular splicing regulator binds to a transcript (mRNA) with an abnormally expanded repeat, and thus a reduced availability of the splicing regulator for normal splicing triggers aberrant splicing.
Patent Literature 1 discloses that 18 compounds including gentian violet inhibited aberrant splicing of at least one of genes associated with myotonic dystrophy. However, there is no disclosure that these compounds can actually improve the symptoms of myotonic dystrophy. There is still no effective and highly safe therapy for myotonic dystrophy, and in the current circumstances, only symptomatic therapies, such as diet therapy, are given to patients depending on the particular symptoms.